1. Field of the Invention
The present invention relates to an automatic pallet exchanger of a machine tool, and more particularly, to an automatic pallet exchanger of a machine tool, which can exactly decide a position of a pallet exchanging operation, and which can improve stability in operation.
2. Background Art
In general, a pallet located in a processing area and a pallet located in a waiting area are exchanged with each other whenever processing is finished. Therefore, a workpiece put on the pallet located in the processing area is returned to the waiting area after completion of the processing in the processing area, and at the same time, a workpiece put on the pallet located in the waiting area is returned to the processing area. To fulfill such work for exchanging the workpieces with each other, a machine tool has an APC (Automatic Pallet Changer).
First of all, the terminology described in the present application is defined as below:
‘Elevating’ means a motion to ascend and descend.
FIGS. 8 and 9 are structural views of a conventional automatic pallet exchanger of a machine tool. FIG. 9 is a sectional view taken along the line of B-B of FIG. 8.
As shown in FIGS. 8 and 9, to exchange a first pallet (P1) located in a processing area 10 and a second pallet (P2) located in a waiting area 11 with each other, an APC arm 40 performs four motions, such as ascent, rotation, stop and descent.
That is, the APC arm 40 performs the steps of ascending a piston 90 in a cylinder 80 with hydraulic pressure, rotating an APC driving shaft 30 standing on an APC body 20 by the medium of a pinion gear 50 by rectilinearly moving a rack 60 by pressure oil induced into an index cylinder 70, stopping the APC driving shaft 30 by a stopper 72 when the APC driving shaft 30 is rotated at an angle of 180 degree, and finishing the pallet exchange by descending the piston 90. Therefore, the first pallet (P1) located in the processing area is transferred to the waiting area, and the second pallet (P2) located in the waiting area is transferred to the processing area, and thereby, the workpieces are exchanged with each other.
As described above, when the rotational motion of the APC arm 40 is stopped by the stopper 72 after the rectilinear motion of the rack 60 is carried out by the pinion gear 50 engaged to the APC driving shaft 30, there occurs a backlash between the engaged teeth of the rack 60 and the pinion gear 50. Such backlash induces backward rotation of the APC arm 40 or generates vibration, and thereby, interrupts a correct position decision and deteriorates durability of APC driving components.
Moreover, in the conventional APC device, only one guide for guiding the ascending motion of the APC arm 40 is mounted at one place. That is, as shown in FIG. 8, the APC arm 40 rises depending on the one guide 200 mounted at one place between the cylinder 80 and the elevating cylinder housing 92, and thereby, the following problem is caused.
That is, as shown in FIG. 8, when biased load is applied to the APC arm 40 by the workpiece (W), there occurs a partial side wear on the guide 200 since the load is concentrated on one side, and thereby, the entire APC driving part is leaned so as to deteriorate a degree of processing.